Apparatus for plating small articles



1931- L. E. FROST ET AL 1,835,643

APPARATUS FOR PLATING SMALL ARTICLES Filed June 29, 1928 III INVENTORS. Les/[e 5 Pros) A; Byron llfil firfde.

' ATTORNEY Patented Dec; 8, 1931 UNITED swvrus PATE NT= OFFICE -LESLIE E. FROST, OF WILKINSBURG, AND BYRON V. MCBRIDE, OF IRWIN, PENNSYL- VANIA, ASSIGNORS TO WESTINGHOUSE ELECTRIC AND EANUFACTURING COMPANY,

A CORPORATION OF PENNSYLVANIA APPARATUS FOR PLATING SMALL ARTICLES Application filed June 29,

Our invention relates to a process and an apparatus for plating a large number of small elements, such as nuts, screws and bolts, with a protective layer of another metal, and more particularly to a process and an apparatus forcoating such articles with an electro-deposited layer of chromium.

An object of our invention is to provide an improved method of coating a large number of small elements with an electro-deposited layer of. another metal.

Another object of our invention is to provide an apparatus and a process by means of which a large number of small articles, such as bolts, nuts or screws, may be economically and uniformly coated with an electro-deposited layer of another metal, such as chr0- mium. I

Another and more specific object of our invention is to provide a process for coating a large number of small elements with an electro-deposited layer of another metal, such as chromium, which consists, essentially, in providing the plating bath with a cathode which consists of a rotatable wire basket or perforated container partially filled with the articles to be plated and passing a current through a suitable platin bath in conjunction with an anode exten ing into andhaving an exterior surface that is substantially concentric with, the surface of the cathode.

In the electro-deposition of some metals, and especially chromium, it is desirable that the anode shall present a surface which is somewhat similar, in contour, to the surface of the article to be coated. Considerable difliculty has, therefore, been experienced in coating small articles, such as screws, bolts and the like, with an electro-deposited layer of chromium because of the differences in the form and shape of the articles to be coated and on account of the fact that the portion of the article which is in closest proximity to the anode and exposed directly to the plating action of the bath receives a heavier coat of the electro-deposited metal than the opposite side.

We have made the discovery that, when small articles, such as screws, bolts, nuts or the like, are placed in a rotatable wire bas- 1928. Serial No.- 289,188.

ket having a comparatively small mesh, or a perforated container, and a current is passed through a bath from an anode, the exterior surface of which has substantially the same contour as the container, the small articles or elements may be economically and uniformly plated.

' Our invention will be better understood by reference to the accompanying drawings, in which;

Figure 1 is a vertical sectional view of a chromium-plating tank, showing the anode partially in elevation, and

Figs. 2 and 3 are side and end elevational views, respectively, of the anode.

Referring to Fig. 1 of the drawings, the numeral 1 designates a plating tank, preferably made of wood and having a lead or other suitable lining 2.

A wire basket or perforated container 3 is provided with a trunnion 4 which extends through an aperture in a supporting member 5 that is mounted upon the.container 1 by means of U-shaped flanges 6. The trunnion consists of a curved portion 8, a supporting arm 9 and a U-shaped member 10. The portion 8, which is preferably curved to conform to the interior surface of the basket,

is supported in a fixed position on the interior of the basket by one end of an arm 9, which extends through an opening in the basket, the other end of the arm 9 being integral with the U-shaped' member 10 which fits over the edge'of the tank. The U-shaped member of the anode is insulated from the tank by any suitable means, such as by a strip of asbestos 11' or by laminated fabric. The bolts, screws or other articles 12 to be plated are placed in the basket 3, all. portions of the basket being insulated from the plating action of the bath except that portion which is in contact with, or comes mto contact with, the articles to be plated during the rotation of the container. We prefer to em loy sheets of asbestos 13 for this purpose alt ough other insulating material, such as a composition consistsing of water-glass and asbestos baked on the portions of the basket to be insulated, has been found satisfactory. Steam coils 14 are provided for maintaining the bath at the proper temperature.

Any suitable plating solution may be employed but we prefer to utilize a bath composed of about 33.3 ozs. of ClllOlIllllIIl tr1-.. oxide and 1 oz. of chromic sulphate to each gallon of water. We have sometimes found it expedient to utilize commercial, ChIOIIllC acid which contains approximately the percentage of chromic sulphate specified. The current density of the cathode is maintained at three amperes per square inch of exposed area of the articles to be plated, but, durmg the plating operation, only about one ampere er square inch of exposed area is available or. plating the articles, as the remainder of the current passes to the exposed portions of the basket. The bath is maintained at a temperature of about to C. It be understood, however, that the composltlon and temperature of the bath and the cathode density may be varied to a reasonable extent without materially afiecting the efficiency of the process.

During electrolysis, the current enters thepositive terminal '15 which is secured to the anode, passes through the anode and solution 16, causing the chromium to be deposited upon the articles to be plated. The current then passes through the wire basket to the negatlve terminal 17. During the passage of the current, the basket 3 is slowly rotated and the small articles are carried up the side of the basket. At a certain height, however,

the articles will have the ten enc to fall, by gravity, to the bottom of the has et where thelr opposite sides will be exposed directly to the plating action of the bath. By continual agitation of the articles, in this manner, all sides will be exposed to the lating action of the bath and will be uni ormly plated.

While we have described a preferred embodiment of our invent-ion, it will be understood that various modifications may be made therein without departin from the spirit thereof. For example, alt ough we have described our process as being particularly adapted for plating small articles with chromium, our improved rocess may also be utilized for plating suc h articles with other metals, such as nickel or cadmium.

It will also be understood that, instead of utilizing a lead-lined wooden tank, a metal tank may be employed or the wooden tank may be lined with any material which is not attacked by the acid bath. The anode may also be formed of other metals, such as iron or steel, although we prefer to employ lead, as it has been. found that the utilization of a'lead anode in the electro-deposition of chromium has a tendency to oxidize any undesirable chromic chromate which may be formed in the bath to chromic acid. The basket 3 may also be formed of perforated metal, or other means may be provided to permit the solution to circulate through the container.

In the event that alarge number of articles are plated or if the articles have the tendency to segregate in the basket and form layers which have a greater or less curvature than that of the basket, the shape of the anode 8 may be correspondingly changed and, in some cases, may even be substantially fiat. In general, however, when the perforated container is rotated, the articles will assume the shape of the container and it is, therefore,

preferred that the anode be slightly curved.

Other modifications of our invention will become apparent to those skilled in the art. We desire, therefore, that only such limitations shall be placed thereon as are imposed by the prior art and the appended claims.

We claim as our invention:

1. An apparatus for electroplating a large number of small articles comprising a tank adapted to hold a suitable electroplating so lution, a perforated metal basket for holding said articles, said basket being insulated from the galvanic action of the bath except at those portions which come in contact with the articles to be plated, the uninsulated portion of the basket, together with said artlcles forming the cathode, and an anode having a surface conforming to the contour of the articles to be plated and extending into said hasket.

2. An apparatus for electroplating a large number of small articles comprising a tank adapted to hold a suitable plating solution, a perforated metallic basket having a c lindrlcal lportion which is closed at one en and partia y open at the other end, said end portions being interiorly insulated from the plating action of the bath, the cylindrical portion of the basket, together with the articles to be plated, constituting the cathode, and

contact, said articles, together with the uninsulated portion of the metallic basket, forming the cathode, and an anode extending through one end of the basket and having an exterior surface which conforms to the surface of the cathode during the rotation of the metallic basket.

4. An apparatus for electroplating a plurality of small articles com rising a tank adapted to hold a suitable p ating solution,

a metallic basket having a perforated cylindrical portion which is closed at one end and open at the other end, thecylindrical portion together with the articles to be plated constituting the cathode, an anode having a surface conforming substantiall to the contour of the cathode and extending into said basket through the end which is partially open. In'testimony whereof, we have hereunto subscribed our names this th day of June,

LESLIE E. FROST. BYRON V. MCBRIDE. 

